This application is based on, and claims priority to, JP PA 2001-332482 filed Oct. 30, 2001, the contents of which are incorporated by reference.
1. Field of the Invention
The present invention relates to a semiconductor device in which, when a semiconductor chip is die bonded onto a package, alignment thereof is performed at the same time.
2. Description of the Related Art
As an example of a semiconductor device, a semiconductor photodetector element having a light detecting function will be explained. Examples of semiconductor photodetector elements include an image pick up CCD (charge coupled device), a line sensor (linear image sensor), a range finding module, etc.
Prior art relating to semiconductor photodetector elements will be explained with reference to the drawings.
An example of a semiconductor photodetector element is shown in FIGS. 6(A) through 6(C) and includes a semiconductor chip 50, leads 51, a package 52, an adhesive for die bonding 53, an optical element structure 54, wires 55, and a cavity 56.
On the surface of the semiconductor chip 50, there is provided a photodetector section 50a. The semiconductor chip 50 is die bonded to the package 52, which is integrally molded with the leads 51, on a die pad section 52a, using an adhesive for die bonding 53, such as epoxy resin. Electrodes 50b on the semiconductor chip 50 and the leads 51 are electrically connected by the wires 55 (for example, gold wires), respectively, and the optical element structure 54 is integrally formed on the package 52.
The optical element structure 54 is formed of transparent resin or inorganic glass with the whole or a part thereof having a parallel flat plate or a lens that is transparent to specific wavelengths of received light. The cavity 56 inside the package 52 is filled with a gas (for example, air) and/or a liquid (for example, silicone oil) that allows the transmission of the light with the specific wavelengths, thereby providing a light detecting function.
A second example of a semiconductor photodetector element, as shown in FIGS. 7(A) through 7(C), is an advanced type of the above-described semiconductor photodetector element.
The semiconductor photodetector element of FIGS. 7(A) through 7(C) includes a semiconductor chip 60 having photodetector sections 60a at two positions at the left and the right thereof, leads 61, a package 62 having a die pad section 62a, a first optical element structure 63 as a parallel flat plate, wires 64, and a second optical element structure 65 including a case 65a operating as both a case and an iris, a left-hand lens 65b, and a right-hand lens 65c. The first optical element structure 63 and the package 62 are bonded together by an adhesive. In addition, the second optical element structure 65 and the first optical element structure 63 are bonded together by an adhesive.
An example of a semiconductor light detecting device, which has been published in JP-A-5-240710, is shown in FIGS. 8(A) through 8(C). The semiconductor light detecting device is assembled with an image sensor chip 71 on a package 70 with package leads 72. The image sensor chip 71 and the package leads 72 are electrically connected by bonding wires 73. On the image sensor chip 71, there is formed a solder bump 74 at a specified position. A tunable optical band-pass filter 75 is positioned for mounting on the image sensor chip 71 by abutting the solder bump 74. The tunable optical bandpass filter 75 and the image sensor chip 71 are bonded together by an adhesive 76, on which a light shielding resin 77 is formed.
An example of a semiconductor light emitting element, which has been published in JP-A-9-8358, is shown in FIGS. 9(A) and 9(B). The semiconductor light emitting element of FIGS. 9(A) and 9(B) includes a semiconductor chip 80 that has become approximately cube-shaped as the area of semiconductor chip 80 has been downsized, thereby becoming tall and unstable. In particular, a lead 81 is provided with a recess 81a in which the bottom of the semiconductor chip 80 is placed. An electrode 80a is provided at the top and the bottom of the semiconductor chip 80, which has a light emitting layer. One electrode 80a is die bonded to the lead 81 at the bottom of the semiconductor chip 80, while the other electrode 80a is electrically connected to another lead 82 by a wire 83. Then, molding with a transparent resin is performed to form a semiconductor light emitting element. An advantage of the semiconductor light emitting element of FIGS. 9(A) and 9(B) is that the die bonding of the semiconductor chip 80 to the lead 81 can be easily performed.
In the semiconductor photodetector element having a light detecting function, as shown in FIGS. 6(A) through 6(C), the semiconductor chip 50 is mounted on the die pad section 52a of the package 52 using a die bonder (not shown). The mounting position of the semiconductor chip 50 to the package 52 depends largely on the performance of the die bonder.
For example, when the semiconductor chip 50 is picked up from a diced wafer by suction of a chuck of the die bonder for mounting on the package 52, there are variations in the position of the picked up semiconductor chip 50 with respect to the chuck or in the position of the chip when placed on the target package 52. Therefore, even when the chuck itself is aligned with high-accuracy, there is still a problem in that the position of the semiconductor chip 50 varies when placed on the package 52.
Moreover, in a die bonder with improved mounting accuracy, the position of the semiconductor chip 50 picked up by the chuck using suction is measured with respect to the position and the direction of the chuck using a measuring method such as image processing, and the position of the package 52 is measured before the semiconductor chip 50 is mounted on the package 52 to minimize misalignment error.
However, the semiconductor chip 50 moves when released from the chuck. Also, when the adhesive for die bonding 53 between the semiconductor chip 50 and the die pad section 52a is cured by heat or ultraviolet light, bonding the semiconductor chip 50 to the die pad section 52a, there arises a problem in that a shock applied during transfer to a curing processing unit, or nonuniform internal stress of the adhesive for die bonding 53 caused in a curing process, results in a shift in the position of the semiconductor chip 50. Similar problems exist in the semiconductor photodetector element shown in FIGS. 7(A) through 7(C) when mounting the semiconductor chip 60 on the package 62.
To cope with the shifting produced when the semiconductor chips 50 and 60 are die bonded, or when a lens (not shown) is combined with the optical element structure 54 in FIG. 6(C), an effective light detecting region of the semiconductor photodetector element is made larger within a margin in anticipation of the shift produced when assembling the semiconductor photodetector element. Thus, the produced shift between the center of the optical system and the center of the light detecting region can be corrected to attain the proper operation.
When the semiconductor photodetector element of FIGS. 7(A) through 7(C) is used, for example, as a range finding module, light beams providing scenes identical to each other are projected onto two linear photodetector sections 60a on the semiconductor chip 60 using the two convex lenses 65b and 65c of the second optical element structure 65, to obtain the distance to the scene using a phase difference between respective projected images. To prevent measuring error in the range finding, the second optical element structure 65 is mounted so that line segments connecting optical centers of the two convex lenses 65b and 65c to the centers of the respective photodetector sections 60a are parallel.
Thus, to eliminate the positional shift or alignment error of the semiconductor chip 60 using a separately provided optical measuring unit, the misalignment between centers of the convex lenses 65b and 65c and the respective photodetector sections 60a is measured. Then, the positions are adjusted to reduce alignment error. Thereafter, the second optical element structure 65 and the package 62 are integrally formed using adhesion. However, measurement of the misalignment between centers of the convex lenses 65b and 65c and respective photodetector sections 60a is not easy, and it is time consuming to perform the adjustment.
Thus, positioning is difficult in the semiconductor photodetector elements shown in FIGS. 6(A) through 7(C).
In addition, in FIGS. 8(A) through 8(C), to position the tunable optical band-pass filter 75 that abuts the solder bump 74, the tunable optical band-pass filter 75 must be integrally fixed by the adhesive 76 while remaining butted against the solder bump 74, which complicates production.
Further, in the semiconductor light emitting element shown in FIGS. 9(A) and 9(B), when the tall and unstable semiconductor chip 80 is fixed at the recess 81a of the lead 81, the semiconductor chip 80 is held in the recess 81a and die bonding is performed while the recess 81a is filled with a material having conductivity (for example, Ag epoxy). This necessitates the recess 81a, which is a square-shaped recess, being sufficiently larger than the semiconductor chip 80. Hence, the semiconductor chip 80 moves in a wide range within the recess 81a, making it difficult to improve the positioning accuracy of mounting the semiconductor chip 80.
It is an object of the present invention to provide a semiconductor device in which positional accuracy during mounting of the semiconductor chip onto the package is not affected by operation of a mounting unit such as a die bonder.
It is another object of the present invention to provide a semiconductor device having a structure in which the position of a semiconductor chip in a package can be easily aligned for die bonding and the position of the semiconductor chip can be maintained with high accuracy during the period in which the chip is being fixed to the package.
Another object of the present invention is to provide a semiconductor device having a light detecting function in which the position of a semiconductor chip in the package can be accurately determined, and the package and an optical element structure can be integrally formed easily with high accuracy by combining and bonding the package and the optical element structure while accurately positioning the optical element structure using a recessed and projected fitting structure.
Additional objects and advantages of the invention will be set forth in part in the description that follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects according to an embodiment of the present invention, there is provided a semiconductor device including a semiconductor chip die bonded on a die pad section of a package, guide projections around a perimeter of the die pad section of the package, and spring projections around the perimeter of the die pad section of the package. Each spring projection is arranged opposite an associated guide projection. The semiconductor chip is pushed against the guide projections by the spring projections to align the semiconductor chip for die bonding on the die pad section. Each of the guide projections is used as a reference for alignment.
The semiconductor chip is disposed on the die pad section by a die bonder and held between the spring projections and the guide projections. The semiconductor chip is pushed against the guide projections by the spring projections for alignment with reference to the guide projections. Therefore, the alignment is unaffected by the positioning accuracy of the die bonder or a package transporting unit, which makes it possible to improve alignment accuracy just by improving positional accuracy of the package or the guide projections.
According to another aspect of the present invention, the guide projections and the spring projections are provided in pairs and a pushing direction of one of the spring projections toward the associated guide projection in a pair crosses another pushing direction in another pair. In this aspect of the present invention, the pushing forces of the guide projections and the spring projections are provided in a lateral direction and a longitudinal direction, and cross approximately perpendicularly to each other. Thus, the semiconductor chip can be fixed to the guide projections and positioned to reduce movement in two directions.
According to another aspect of the present invention, the guide projections and the spring projections are provided in pairs in which each pushing direction of the spring projections toward the associated guide projections is in the same direction. In this aspect of the present invention, the guide projections and the spring projections provide a pushing force in only the lateral direction or the longitudinal direction. Thus, although the semiconductor chip is fixed to the guide projections to restrict movement in the pushing direction, movement of the semiconductor chip is not restricted in the direction approximately perpendicular to the pushing direction. This is effective when strict positioning accuracy is not required in the movable direction, allowing positioning accuracy of the die bonder. In addition, the pushing force provided by the guide projections and the spring projections is sufficiently strong that movement of the semiconductor chip in the movable direction is not easy, making it possible to sufficiently fix the position of the semiconductor chip, even when the adhesive for die bonding is being cured.
According to another aspect of the present invention, the package has a recess with a bottom that is lower than the die pad section between the spring projections and the guide projections at least at a front of the guide projections. When the guide projections vertically project directly from the same face as that of the die pad section of the package, a somewhat lifted fillet produced during resin molding, or particles or debris, may be present at a square corner formed between the package and the guide projections, if the recess is not provided. The fillet or particles between the semiconductor chip and the package may cause misalignment of the semiconductor chip on the package. However, with the recess provided, the fillet is formed in the recess, preventing the semiconductor chip from abutting the fillet. Moreover, the particles drop into the recess, preventing the semiconductor chip from abutting the particles. Thus, it becomes possible to maintain accurate alignment.
According to another aspect of the present invention, the package has a recess with a bottom that is lower than the die pad section, the recess surrounding a bottom of the spring projections. When the spring projections vertically project directly from the same face as that of the die pad section of the package without the recess being provided, the semiconductor chip, the height of which is determined by the die pad section of the package, butts against the spring projections at a square corner of a root thereof. This occurs at a portion of the spring projection having a limited amount of bending, making it difficult to fit a large semiconductor chip into the die pad section, which may cause misalignment of the semiconductor chip. However, with the recess provided, the spring projections bend sufficiently at a portion against which the semiconductor chip abuts. Also, the recess may surround each spring projection to further facilitate bending. Thus, even a large semiconductor chip may be fitted onto the die pad section. In addition, as described above, particles or debris drop into the recess so that the semiconductor chip does not abut the particles. Thus, it becomes possible to maintain accurate alignment.
According to another aspect of the present invention, each of the spring projections and the guide projections has a guiding sloped portion on a side facing the die pad section to guide the semiconductor chip. Even though the semiconductor chip may be misaligned as it is being vertically placed on the die pad section by the die bonder, the semiconductor chip is guided between the spring projections and the guide projections by the guiding sloped portion. Therefore, the semiconductor chip can be accurately fitted into the die pad section.
According to another aspect of the present invention, an optical element structure is mounted on the package and has an optical system that positions a focal point at the semiconductor chip. A recessed and projected fitting structure is provided to align the optical element structure onto the package. The recessed and projected structure includes a fitting recess provided in the package and a fitting projection provided in the optical element structure. The fitting recess and the fitting projection are fitted together to align the optical element structure onto the package.
In this aspect of the present invention, the optical element structure is positioned and mounted on the semiconductor chip, which has been accurately positioned on the package, by the recessed and projected fitting structure. For example, an optical axis of a photodetector section of the semiconductor chip having a light detecting function and an optical axis of the optical element structure (for example, a convex lens) are made to coincide with each other. This offers an advantage in that alignment adjustments are completed at the same time the mounting is completed. The package and the optical element structure may include the fitting recess and the fitting projection, respectively, or the package and the optical element structure may include the fitting projection and the fitting recess, respectively, as required.
According to another aspect of the present invention, in a direction in which strict alignment of the optical element structure is required, an adjustment clearance area in the recessed and projected fitting structure is enlarged, and in a direction in which no alignment of the optical element structure is required, the adjustment clearance area is reduced. In this aspect of the present invention, if a semiconductor device requires more precise alignment in one direction, the adjusting range of the optical element structure is increased in the direction in which more precise alignment is required. In the direction in which no alignment or less precision is required, the adjusting range is narrowed. This enables an adjustment to be carried out when adjustments are limited to one direction.
According to another aspect of the present invention, the package and the optical element structure are fixed to each other using an adhesive. After adjustments are completed, the package and the optical element structure are integrally fixed by bonding to maintain the alignment.
According to another aspect of the present invention, a method of aligning a semiconductor chip on a die pad of a semiconductor device is provided including forming guide projections around a perimeter of the die pad; forming spring projections around the perimeter of the die pad, each spring projection being paired with an associated guide projection; placing the semiconductor chip on the die pad between the guide projections and the spring projections, the spring projections bending to receive the semiconductor chip and pushing the semiconductor chip against the guide projections to align the semiconductor chip; and die bonding the aligned semiconductor chip to the die pad.
These, together with other aspects and advantages that will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.